[PATCH] vdso: randomize the i386 vDSO by moving it into a vma

Move the i386 VDSO down into a vma and thus randomize it.

Besides the security implications, this feature also helps debuggers, which
can COW a vma-backed VDSO just like a normal DSO and can thus do
single-stepping and other debugging features.

It's good for hypervisors (Xen, VMWare) too, which typically live in the same
high-mapped address space as the VDSO, hence whenever the VDSO is used, they
get lots of guest pagefaults and have to fix such guest accesses up - which
slows things down instead of speeding things up (the primary purpose of the
VDSO).

There's a new CONFIG_COMPAT_VDSO (default=y) option, which provides support
for older glibcs that still rely on a prelinked high-mapped VDSO.  Newer
distributions (using glibc 2.3.3 or later) can turn this option off.  Turning
it off is also recommended for security reasons: attackers cannot use the
predictable high-mapped VDSO page as syscall trampoline anymore.

There is a new vdso=[0|1] boot option as well, and a runtime
/proc/sys/vm/vdso_enabled sysctl switch, that allows the VDSO to be turned
on/off.

(This version of the VDSO-randomization patch also has working ELF
coredumping, the previous patch crashed in the coredumping code.)

This code is a combined work of the exec-shield VDSO randomization
code and Gerd Hoffmann's hypervisor-centric VDSO patch. Rusty Russell
started this patch and i completed it.

[akpm@osdl.org: cleanups]
[akpm@osdl.org: compile fix]
[akpm@osdl.org: compile fix 2]
[akpm@osdl.org: compile fix 3]
[akpm@osdl.org: revernt MAXMEM change]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@infradead.org>
Cc: Gerd Hoffmann <kraxel@suse.de>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Zachary Amsden <zach@vmware.com>
Cc: Andi Kleen <ak@muc.de>
Cc: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 18 insertions, 12 deletions

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 0137ec4c1368..0a163a4f7764 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -122,6 +122,11 @@ struct mem_size_stats
         unsigned long private_dirty;
 };
 
+__attribute__((weak)) const char *arch_vma_name(struct vm_area_struct *vma)
+{
+        return NULL;
+}
+
 static int show_map_internal(struct seq_file *m, void *v, struct mem_size_stats *mss)
 {
         struct proc_maps_private *priv = m->private;
@@ -158,22 +163,23 @@ static int show_map_internal(struct seq_file *m, void *v, struct mem_size_stats
                 pad_len_spaces(m, len);
                 seq_path(m, file->f_vfsmnt, file->f_dentry, "\n");
         } else {
-                if (mm) {
-                        if (vma->vm_start <= mm->start_brk &&
+                const char *name = arch_vma_name(vma);
+                if (!name) {
+                        if (mm) {
+                                if (vma->vm_start <= mm->start_brk &&
                                                 vma->vm_end >= mm->brk) {
-                                pad_len_spaces(m, len);
-                                seq_puts(m, "[heap]");
-                        } else {
-                                if (vma->vm_start <= mm->start_stack &&
-                                        vma->vm_end >= mm->start_stack) {
-
-                                        pad_len_spaces(m, len);
-                                        seq_puts(m, "[stack]");
+                                        name = "[heap]";
+                                } else if (vma->vm_start <= mm->start_stack &&
+                                           vma->vm_end >= mm->start_stack) {
+                                        name = "[stack]";
                                 }
+                        } else {
+                                name = "[vdso]";
                         }
-                } else {
+                }
+                if (name) {
                         pad_len_spaces(m, len);
-                        seq_puts(m, "[vdso]");
+                        seq_puts(m, name);
                 }
         }
         seq_putc(m, '\n');